I agree with you. I suspect them of being paid and not telling it to other people to avoid a new ban of the signature and their accounts. But how could we check that? Is there a list of the current participants somewhere?
Read:
Probably the closest you're going to get without scraping userprofiles yourself.
Yobit doesn't maitain a (public) list of participants themselves.
I really doubt these users are actually getting paid though, otherwise we would've seen a lot more alt accounts being active wearing this signature, considering they don't care about red trusted users etc.